1. Field of the Invention
The present invention relates to shaft structures for rotational support by a non-ball type bearing and having a smaller contact surface with the non-ball type bearing, thereby reducing the frictional area.
2. Description of the Related Art
There are two types of commonly known bearings for rotational support the shaft of a miniature fan or motor. Namely ball bearings and non-ball type bearings. A ball bearing generally includes an inner race for receiving the shaft and an outer ring securely engaged in a hole of a bearing seat, thereby allowing smooth rotation of the balls of the ball bearing. Non-ball type bearings are made of abrasion-resistant material, such as copper bearings, oil-pregnant bearings, self-lubricating bearings, etc. The non-ball type bearing has an inner bore in non-tight contact with the shaft. During use the friction between shaft and bearing results in wears. After long time use the gap between shaft and bearing increased thereby resulting in skew problem of the shaft during rotation. In addition, the rotational noise is increased and the operating life of the bearing and the shaft are shortened.
Taiwan Utility Model Publication No. 360341, issued on Jun. 1, 1999 and entitled "IMPROVED FAN STRUCTURE", discloses a fan impeller with a cap body underneath and a shaft extended from a center of the cap body. A tubular bearing seat is provided in a center of a fan housing for fitting the shaft. An annular groove is defined between the cap body and an end of the shaft. The shaft includes an annular recessed section. A bearing sleeve is mounted around the shaft to define a first oil reservoir. The inner periphery of the bearing seat includes a number of grooves defined in parts corresponding to the bearing, thereby defining a second oil reservoir. The oil reservoirs store lubrication oil. The annular recessed section of the shaft may reduce the frictional area between the shaft and the bearing. Nevertheless, the shaft and the bearing are in non-tight contact and thus have a clearance therebetween. The shaft is supported at areas other than the annular recessed section during rotation. These two areas are circular and are thus in continuous frictional contact with the bearing.